This invention generally relates to projectiles having explosive charges therein and more particularly to a pyrotechnically initiatied explosive (PIE) projectile which is ignited by a pyrotechnic incendiary charge located in the nose of the projectile. More specifically, the invention relates to a barrier which prevents preignition of the pyrotechnic charge from relative frictional movement between the projectile components.
The potential for premature ignition of incendiary or explosives contained in projectiles during handling and/or acceleration has long been recognized. Various attempts to alleviate this problem are exemplified by the following U.S. patents.
U.S. Pat. No. 47,544 to Hotchkiss discloses an explosive ordnance shell having transverse ribs to partition the explosive charge so as to limit friction between the shell contents during spin up.
U.S. Pat. No. 373,459 to Howell also discloses an explosive shell having transverse diaphrams between and separating the explosive charge.
U.S. Pat. No. 383,223 to Graydon discloses an explosive shell containing separated explosive charges. The charges are separated by transverse partitions which also may have perforations to conduct the flame between the charges.
U.S. Pat. No. 3,720,169 to Johnson et al discloses a projectile having two nose incendiary charges separated from one another by a partition disk.
U.S. Pat. No. 4,876,964 to Strandli et al discloses an incendiary containing projectile which has an interior coating or lining to prevent inadvertant ignition of the incendiary if the projectile is dropped.
Several designs of PIE projectiles have been developed in recent years for small caliber ammunition with varying degrees of success. One such projectile is disclosed in U.S. Pat. No. 4,625,650, assigned to the assignee of the present invention. This copper jacketed explosive bullet for penetrating light armor has an inner tubular hard heavy metal penetrator body filled with a high explosive. It has a nose portion forward of the penetrator which is filled with an incendiary material. The incendiary is designed to ignite upon target impact, in turn igniting the explosive after penetrating light armor. Around the outside of the penetrator and nose portion is an outer copper jacket which forms the final aerodynamic shape of the bullet.
Another PIE projectile is disclosed in U.S. Pat. No. 4,353,302. This patent discloses a projectile having a tubular steel body filled with explosive and also having a nose filled with an incendiary ignition material. Also within the tubular body is a subcaliber, solid tungsten penetrator core for the penetration of light armor.
During spin-up of these types of projectiles in the weapon bore, there is some relative movement between the jacket and the tubular body. This movement may result in premature ignition of the incendiary material and the explosive in the weapon bore which is highly undesirable.
The cause of the preignition is not the relative movement per se. It is due to the presence of small amounts of incendiary material between the jacket and the tubular body at the location of relative movement. The incendiary material may frictionally cling to the jacket sidewall as a result of the charging operation. Under assembly pressures, the material may also flow into undesired locations where normal part tolerances provide an opening. The friction from relative movement, occuring during spin-up, ignites this small amount of incendiary which in turn ignites the main incendiary and/or explosive charge.
The present invention prevents preignition by providing a flexible seal ring partition between the tubular body and the jacket where the incendiary joins with the tubular body and the jacket, and by designing the seal ring to scrape the inner wall of the jacket during installation to remove residual incendiary material from the wall of the jacket. Thus there is no residual incendiary material on the jacket wall when the tubular body is installed in the jacket. Further, the shape of the seal ring tends to guide itself during insertion into the jacket to ensure coaxial alignment of the seal ring with the jacket.
The seal ring of the present invention comprises a ring shaped plastic body generally symmetrical about a central axis. The body has an outwardly flared front collar portion and an outwardly flared rear skirt portion which are integrally joined to a central tubular portion. The central portion has an inwardly projecting curved lip protruding inward toward the central axis. The curved lip has a smooth concave surface oriented forwardly toward the projectile nose.
The seal ring is designed to be installed within the jacket after the incendiary material is deposited in the nose end of the jacket and prior to the insertion of the tubular hard metal body containing the high explosive. The seal ring is sized so as to frictionally fit into the projectile jacket. The front collar portion is sufficiently large in diameter so that it is constricted during insertion within the jacket to scrape or swab along the inner wall of the jacket to remove any incendiary material which has adhered to the inner wall. Thus, all of the residual incendiary is moved to the forward, proper location during component assembly. The front collar portion is also short enough in length so that the material of the collar does not wrinkle when it conforms to the inner wall of the jacket.
The rear skirt portion is sized slightly larger in diameter than the front collar portion so as to act like a shuttle cock during seal insertion. This keeps the seal in proper axial alignment. The rear portion is also segmented or provided with cutout portions to avoid wrinkling when it is constricted during insertion. The rear portion is sized to fit over the front end of the tubular body and is ultimately swaged between the tubular metal body and the jacket to seal this interface.
Finally, a central bore through the seal ring permits an incendiary interface with the high explosive charge to maintain continuity of the explosive train. The size of this bore may be varied to control the detonation efficiency by providing greater confinement of the high explosive.
Other objects, features and advantages of the invention will become more apparent from consideration of the following detailed description when taken in conjunction with the drawing and appended claims.